The MySQL support is for Percona database also or only for Oracle MySQL?
Right now we are only supporting vanilla MySQL but plan to expand support out to different flavors moving forward. That being said it seems Percona database might be compatible with MySQL which means it could work today. I would try it out, but no promises.
Is Oracle database supported as well (not MySQL)?
It is not supported, but there are not technical obstacles to adding it or any other DB that supports multirow transactions.
How much work would adding and Oracle (or PostgreSQL) database support involve?
The API is well defined. So actual implementation effort is not very large. I would say one to two person months. Additionally it requires investing into testing to ensure production quality.